1. Field of the Invention
In recent years, small scale and light electronic devices with multi-functionality and high functionality are becoming widespread and a greater level of integration of installed electronic components is being demanded. In response to such demands, the number of each type of electronic component being manufactured as a semiconductor device is increasing. Consequently, small scale and light electronic devices such as a sensor etc for detecting mechanical quantity are being manufactured using semiconductor devices apart from semiconductor devices manufactured as circuit components. For example, A moving part which displaces is formed according to an external force on a semiconductor substrate in an acceleration sensor or angular velocity sensor having a small scale and simple structure using MEMS (Micro Electro Mechanical Systems) technology, and a mechanical sensor (called a piezo resistor sensor) in which the displacement of this moving part is detected using a piezo resistor is realized.
A specific example of the above stated mechanical sensor is shown in FIG. 10 and FIG. 11. FIG. 10 is a planar diagram which shows a triaxial acceleration sensor 100 which uses a piezo resistor. FIG. 11 is a planar diagram which shows the structure of an expanded region A part shown in FIG. 10. In FIG. 10, an acceleration sensor 100 is arranged with a substrate 101 which includes an element forming region 102 in which sensor elements having the above stated moving part are formed. A plurality of piezo resistors 103 which detect the displacement of the moving part in a triaxial direction XYZ are arranged in 4 locations within this element forming region. In addition, a plurality of connection pads 105 is formed in a periphery region of the element forming region 102. The plurality of connection pads 105 are a group of pads for electrically connecting the interior of the acceleration sensor 100 with an external circuit.
In FIG. 11, the piezo resistors 103 within the element forming region 102 are electrically connected with the connection pads 105 via a plurality of metal wires 104. The metal wires 104 externally output a detection signal of the piezo resistors 103 from the connection pads 105 and supply a current and voltage etc to the interior of the acceleration sensor 100.
The package size of the acceleration sensor 100 tends to become miniaturized and the wire width of the metal wires 104 and size of the connection pads 105 also tends to become miniaturized. As a result, when the wire width of each metal wire 104 and the size of each connection pad 105 are different, variation in resistance values of a part which includes the metal wires 104 and connection pads 105 is produced and causes a current which flows in each piezo resistor 103 to fluctuate. Consequently, the variation in resistance values of the part which includes the metal wires 104 and connection pads 105 influences the detection sensitivity of the sensor parts.
An acceleration sensor which reduces the influence on the detection sensitivity of a sensor due to variation in resistance values as stated above is disclosed in Japan Laid Open Patent 2003-101033. In this acceleration sensor, each resistance value becomes approximately equal by adjusting the shape of an extraction electrode pattern which connects the piezo resistors with external connection terminals.
2. Description of the Related Art
However, because a mechanical sensor which includes an acceleration sensor such as that stated above, is used for a variety of purposes, the arrangement of a connecting external circuit and connection terminals of an external IC are also wide and varied. As a result, it is necessary to align the arrangement of connecting pads of a mechanical sensor according to the function and arrangement of connection terminals arranged on an external circuit or external IC. That is, it is necessary to change the design of the internal wiring pattern according to the arrangement of connection terminals of a connecting external circuit or external IC which restricts the level of design freedom and also causes an increase in manufacturing costs of the mechanical sensor.
In the acceleration sensor 100 shown in FIG. 10 and FIG. 11, a plurality of piezo resistors forms a bridge circuit which corresponds to each triaxial XYZ respectively and acceleration is detected by detecting a change of current which flows in each bridge circuit according to the acceleration which is applied. That is, the resistance values of each piezo resistor changes according to a XYZ triaxial displacement of the moving part, and the XYZ triaxial acceleration is detected by a change in the current which flows when each bridge circuit is in a nonequilibrium state. As a result, in a state in which an external force is not applied to the acceleration sensor 100, it is necessary to design a wire pattern so that an equilibrium state in which a current does not flow in each bridge circuit is maintained while also considering the resistance value of a wire which connects each piezo resistor with a connection pad.
Therefore, design and manufacture is difficult due to the above reasons as in the acceleration sensor 100 shown in FIG. 10 and FIG. 11 when changing the internal wiring pattern according to the function and arrangement of a connecting external circuit or external IC in the case where a wire pattern is formed by one layer of metal wires. That is, according to a request from the external circuit or external IC, it requires time and effort to change a wiring pattern design and prepare a mask suitable for the design change, the design burden and manufacturing burden is increased leading to an increase in manufacturing costs.